A generator with a multi-polar rotor of the aforementioned type is disclosed in German Utility Model No. DE 1811389 (U). This generator includes a rotor, formed by a central arbour that carries two flanges made of magnetic material, at the periphery of which permanent magnets with alternating polarity are arranged, six per flange. The rotor thus includes twelve very small magnets, which are independently secured to one of the two magnetic rotor flanges. The generator also includes two or three flat coils arranged with an angular shift of 120° relative to the axis of rotation of the generator. When the rotor is rotating, the permanent magnets pass opposite the coils. In the embodiment shown, the central axis of the magnets passes approximately through the central axis of the coils. While rotating, the rotor thus induces an electric current in the coils, which is used to power an electronic circuit of a timepiece movement. This electric energy can be stored in a rechargeable battery or in a storage capacitor.
The generator disclosed in DE Utility Model No. 1811389 (U) can certainly efficiently produce an electric current for powering an electronic timepiece circuit and control a generator of this type such that it rotates at a constant speed synchronously with a time base that it powers. However, this generator has various major drawbacks. First of all, it is relatively complex and onerous to manufacture. Indeed, twelve very small magnets have to be supplied and then individually secured in a uniform manner to the periphery of the two magnetic rotor flanges. Next, this generator has a relatively large inertia with the two disc-shaped flanges each carrying six magnets at their periphery. The higher the level of inertia, the more sensitive the generator is to shocks (which means it has to rotate at a certain speed to prevent a shock from stopping it). It will also be noted that the starting torque is also relatively high as is the minimum torque necessary for the generator to operate synchronously.